Stabilization of polyvinyl butyral resins



to the present invention Patented Dec. 14, 1948 STABILIZATION OFPOLYVINYL BUTYRAL RESIN S Gain 8. Stamatoii', Nutley, N. 1., assignor toE. I.

du Pont 'de Nemours Dc}, a corporation of No Drawing.

Claims.

This invention relates to a process for the stabilization of polyvinylbutyral resins and, more particularly, to the production of polyvinylbutyral resins possessing a very high degree of stability towardsdiscoloration and freedom from odorous characteristics.

Polyvinyl butyral resins which are derived from the condensation ofbutyraldehyde with the water-soluble hydrolysis product of polyvinylester or with polyvinyl alcohol, have attained a position ofconsiderable commercial importance. Until recently the major commercialutilization of these resins has been as an interlayer material in theproduction of safety glass. Recently, however, other commercial uses andapplications of these resins have been' developed other than asinterlayers for safety glass. Such applications include the use ofpolyvinyl butyral resins as substitutes for rubber in the production ofwaterproof fabrics, for use as an'ingredient in the production ofpressure-sensitive adhesives, and for use as films'for wrapping food andthe like. f

Obviously, polyvinyl butyral resins produced for use as interlayermaterials for production of safety glass must possess a high degree ofcolor stability and clarity. on the other hand, certain othercharacteristics possessed by these products such as odor have beensubstantially entirely disregarded heretofore. A large majority of thenew uses being developed for these resins require that the materialpossess not only a high degree of color stability and clarity, butlikewise substantially complete freedom from any odor characteristics.

An object of the present invention is to provide a process wherebypolyvinyl butyral resins may be stabilized while suspended in the formof discrete particles in a water medium, to yield a product possessingdesirable color, clarity and odor characteristics. Another object is toprovide a specific class of materials which may be employed inconjunction with this process to impart good color stabilitycharacteristics to the herein considered resins. Other objects will beapparent from the description of the invention given hereinafter.

The above objects are accomplished according by suspending a crude,water-insoluble polyvinyl butyral resin, preferably in finely dividedfor in a preponderantly water solution maintained at a pH of 6.0-7.5 andan alkalinity of between 100 and 200, and, preferably after the resin issubstantially neutralized, dissolving in the water solution at least0.04 by Company, Wilmington,

Delaware Application October 16, 1944, Serial No. 558,982

weight of the resin, of a saturated aliphatic amine having two primaryamino groups, and further subjecting the resin to the action of thesolution until the resin is stabilized. More specifically, the solutionis agitated throughout the treatment as otherwise the resin particleswould tend to settle out, and the solution is maintained at atemperature of -100 C.

The herein, considered polyvinyl butyral resins are thosewater-insoluble products obtained by the condensation of butyraldehydewith a ma terial which is substantially identical to that produced bythe hydrolysis of a polyvinyl ester of a monohydric carboxylic acid toyield a watersoluble product. These latter materials are referred to bythe art as polyvinyl alcohol" although they generally, but notnecessarily, contain in addition to a preponderance of hydroxyl groups,a minor groups, normally acetyl groups since polyvinyl acetate ispractically always the polyvinyl ester saponified. The term polyvinylalcohol," as 7 used herein, is to be understood as possessing thisconnotation.

vDue to the method of preparation, these polyvinyl butyral resins, intheir crude form before stabilization, invariably contain acid residueswhich must be neutralized in the course of the stabilization treatment.The process of the present invention, while applicable to thesepolyvinyl resins prepared by various processes, is particularlyapplicable to the stabilization of crude resins which have been producedby an aqueous condensation process, i.,e., by the. condensation ofpolyvinyl alcohol in a preponderantly water solution with butyraldehydein such manner as to producepolyvinyl butyral resin in the form offinely divided discrete particles as disclosed in applicant's copendingapplication Serial No.

479,055, filed March 13, 1943, now Patent 2,422,754, June 24, 1947. Suchpolyvinyl butyral resins may possess a composition containing 30% orless of hydroxyl content calculated as polyvinyl alcohol,

an ester content of less than 10% calculated as polyvinyl acetate, andan acetal content of more than calculated as polyvinyl butyral.

In the following examples wherein all parts are given by weight unlessotherwise noted, there are illustrative specific preferred embodimentsof the present invention:

Example I A resin suspension resulting from the aqueous condensation ofpolyvinyl alcohol and loutyraldehyde and comprising suspended particlesof a proportion of unsaponified ester polyvinyl acetal resin having thefollowing approximate analysis:

' Per cent Polyvinyl acetate 1 Polyvinyl alcohol 13 Polyvinyl butyral 86Per cent Polyvinyl butyral resin Methanol 1 -2.5 Butyraldehyde 0.2-0.3Sulphuric acid Trace Acetic acid -1.-- Trace Water Remainder 1.0%, byweight of the acetal resin in the suspension, of methyl acetate is addedto the suspension and is followed by about 0.75% of sodium hydroxidedissolved in a small quantity of water. The addition of the sodiumhydroxide is accomplished gradually over a period of about two minutesand in such manner as to maintain the hydrogen ion concentration of thesuspension between a pH of about 6.0 and 7.5, and not as high as 8.0 asmeasured by a glass electrode. The alkalinity of the suspension ashereinafter defined will be found to be of a value: between 100 and 200.The resin suspension is then heated to 85 C. and allowed to agitate forfifteen minutes, at the end of which time the acid residues in the resinare substantially neutralized and 0.1% oi diethyl cyciohexylamine, byweight of the acetal resin, is added over a period of two to threeminutes and is followed in five minutes by 0.1% .01 ethylenediamine byweight of the acetal resin.

The stabilization oi the resin is then completed by continuing theagitation for thirty-five minutes during which time the temperature ismaintained at about 85 C. The resin contained in the suspension is thenwashed to a, final alkalinity oi between and and the resin is isolatedaccording to established practice. The dry powdered resin thus producedpossesses substantially no odor and is characterized by the fact ityields excellent results when subjected to the heat stability and chip"tests described below.

In another case conducted in a fashion similar to that given above, withthe exception that the pH of the water solution is allowed to attain avalue of 8.5, a polyvinyl butyral resin product is isolated from thewater solution. The resin so treated, although possessing good colorstability as measured by the "heat stability" and chip tests possesses astrong, disagreeable, characteristic odor.

In still another case conducted in a manner analogous to that givenabove, but in which the ethylenediamine is omitted and in which the pHis maintained between 6 and 7 throughout the treatment, a resin productis isolated which, although possessing good characteristics with respectto the "chip" test, failed with respect to the "heat stability" test.

In the above example and throughout the specification, the heatstability" test consists in placing about 1 gram of the resin upon aglass plate 2 inches by 3 inches in dimensions, evenly and thinlydistributing the resin contained thereon and thereafter placing theglass plate and the resin in a mechanical convection oven maintained ata temperature of 125 C., and allowing the resin to remain there (or fourhours. To pass this test the resin should exhibit substantially no colorchange or at most a change to a very slight cream color upon beingsubjected to this test. Ii the resin develops a yellow color or somedeeper shade, for example, a brown color, the resin fails the test.

The second test mentioned above is called the "chip" test and consistsin placing 10 grams of the resin in a 2 inch compression mold and sub-,iectlng the same to a pressure of 2500 lbs. per square inch at atemperature of 185 C. for two minutes. To pass this test satisfactorily,the resin chip, when removed from the die, should be substantiallycolorless and clear. Ii the molded chip is characterized by colorgreater than a very light yellow or possesses a haze, it fails thistest.

Example I! A polyvinyl butyral resin suspension containing a resin ofthe following composition:

Per cent Polyvinyl acetate l Polyvinyl alcohol 19 Polyvinyl butyral 80is stabilized by a procedure similar to that oi Example I, except thatsodium bicarbonate is employed in lieu oi the methyl acetate and sodiumhydroxide of Example I in order to adjust the pH and alkalinity. Theproduct thereby obtained possesses good color stability and odorcharacteristics,

Example III 1,000 parts of a polyvinyl butyral resin slurry having acomposition approximately the same as that indicated in Example I, arecharged into a suitable reaction vessel equipped with means foreiiicient agitation. Suflicient sodium bicarbonate is added to theagitated suspension to impart an alkalinity of 100 to the same. The pHof the resulting solution at this point is found to be about 6.8. Thisresin suspension is then heated for fifteen minutes at C. whilevigorously agitated after which 0.07 part of diethylenetriamine areadded. The suspension is then washed and isolated as indicated inExample I. The resulting polyvinyl butyral resin possesses no detectableodor characteristics and exhibits good color stability characteristics.

It will be understood that the above examples are merely illustrativeand that the present invention broadly comprises stabilizing crude,water-insoluble polyvinyl butyral resins by subjecting them to theaction of a preponderantly water solution maintained at a pH of 6.0-7.5and an alkalinity of between and 200, said solution, at least in thelatter stage of the treatment, having dissolved therein a saturatedaliphatic amine having two primary amino groups.

It will be evident from the foregoing Examples that the success of thepresent invention derives from the neutralization of the crude polyvinylbutyral resin in a water suspension whose hydrogen content andalkalinity is adjusted to a specific value and to the employment oi. asaturated aliphatic amine possessing two primary amino groups inconjunction with this water solution. Thus, it a. pH appreciablyin'excess of 7.5 be

throughout the stabilization Acme:

present in the water suspension, during the process of stabilization theresin will develop a As a matter of practical operation, the watersolution should be adjusted and maintained at a pH of 6.0-3.5 although apH even in slight excess of 7.5 but below 8.0 can be tolerated.

The examples also illustrate that, although odorless resins may beobtained by neutralization at pH values below 8.0, satisfactory colorstability will not result unless a saturated amine of the type hereinconsidered in quantities greater than 0.04%, by weight of the resin, ispresent in the water solution during the stabilization treatment afterthe resin is substantially neutralized. Such amines adapted for use inthe present invention include ethylenediamine, hexamethylenediamine,propylenediamine, triethylenetetramine and diethylenetriamine. Otherwater-soluble organlc neutralizing agents such as diethylcyclohexylamine, diphenyl guanidine, diphenyl amine, and the like may beemployed in conjunction with the amines mentioned above provided thelatter are present in the suspension medium in the con-' centrationindicated.

Except for reasons of economy, an appreciable excess of the amine may beused: also, it may be added to the water solution at the beginning ofthe stabilization treatment although, in such instances, due allowancemust be made for loss of eifective amine concentration because of reaction with acid residues contained in the crude resin. However, to makethe most effective and economical use of the amine, it is preferred toadd the amine after the resin is substantially neutralized. In anyevent, the water solution must contain after the resin is substantiallyneutralized, at least 0.04 of a, saturated aliphatic amine, by weight ofthe resin.

The sodium hydroxide employed in Example I and the sodium bicarbonate ofExample If function as alkali neutralizing agents, serving to neutralizeresidual, occluded acid and to help stabilize the resin. The methylacetate employed in.

Example 1 functions as a buffer material in order to permit thealkalinity of the solution to rise to a sufilclent fi ure while thehydrogen ion concentration is maintained within the necessary limits.Other well known strong alkaline materials such as potassium hydroxide,trisodium phosphate and sodium carbonate in conjunction with otherbuffering materials such'as sodium acetate may be substituted for thesodium hydroxide-methyl acetate combination of Example 1. Furthermore,other single compounds such as sodium bicarbonate .which themselvesfunction both as buffering materials and alkaline neutralizingmaterials, i. e., sodium acetate, quaternary ammonium salts and thelike, may be substituted for these materials. In any event, the alkalineneutralizing and buffering material used should be employed in aconcentration which will maintain the dispersion medium at the properhydrogen ion concentration and alkalinity level process. Obviously,

the materials used as neutralizing and bufl'ering agents should notdiscolor the resin, should not impart haze to the resin, and should bewatersoluble.

The term "alkalinity" as used throughout this specification refers tothe potential basic or alkaline characteristics of the aqueousdispersion medium. Because of the discussed buil'ering action present inthe medium, alkalinity is not expressible in such terms as pH orhydroxyl ion concentration. Consequently, the term alkalinity as usedherein is defined as the number of cubic centimeters of 0.01 normalhydrochloric acid required to neutralize 100 grams of the reactionsuspension using bromphenol blue as the indicator. This value may bereadily determined by neutralizing 5.0 grams of the suspension with 0.01normal hydrochloric acid, using promphenol blue as the indicator.

The exact temperature employed during the stabilization process is notcritical. The speed of stabilization is increased through the use ofincreased temperatures and, consequently, temperatures appreciably below0., although not inoperative, are undesirable because of the extendedperiod of time necessary for stabilization. On the other hand, the upperpractical limits for temperature is that of the boiling point of water,i. e., 100 C. It has been found preferable to employ a temperaturebetween C. to 85 C. throughout the course of the stabilization.

The duration of the treatment of the resin cannot be defined withinprecise limits since it is dependent upon many variable conditions aswell as the degree of stabilization necessary. In general, the treatmentwill be continued until the resin is satisfactorily stabilized asdetermined by testing samples taken from time to time during the courseof the stabilization treatment. Once the minimum duration of thetreatment is established for any given set of conditions, obviouslytesting of each batch will not be required. As pointed out above, thetemperature of the water solution influences the duration of thetreatment to obtain satisfactory stabilization of the resin. Thephysical form oi the resin is another important factor sincestabilization will proceed more rapidly with a finely divided resin ascom pared to a resin in the form of coarser particles.

Again, the particular resin being treated and the method by which it hasbeen prepared, may influence the time required for treatment. Thespecific examples show typical times for the stabilization of polyvinylbutyral resins in finely divided form. v

The time required for treatment of the resin to bring it to a pointwhere it is substantially neutralized also will vary considerablydepending upon conditions. There is no necessity for establishing thispoint particularly accurately since there is no harm in adding the aminesomewhat after the resin has been substantially neutralized or evenbefore the resin is neutralized, providing in the latter case someexcess of the amine is added as a safety factor. As shown in theexamples, the resin is ordinarily substantially neutralized, so that itis economical to add the amine, after the treatment has gone on forabout fifteen minutes or so.

Throughout this specification, the medium in which the polyvinyl acetalresin is suspended during stabilization has been referred to as a wateror as a preponderantly water suspension medium. It is to be understoodthat this medium does not consist wholly of water and dissolved solidmaterials but may comprise adventitious liquid components resulting fromprevious processes to which the resinous condensation material has beensubiectedaduring its "course of production. Such material? areexemplified by the methanol and butyraldehyde disclosed in Example 1.Accordingly, the term water suspension medium" or "preponderantly watersuspension medium" when used in this specification shall be taken tomean a water solution composed mainly of water and which possesses asolvency reaction upon polyvinyl acetal resins substantially equivalentto that of water.

An advantage of the present invention is that it makes possible theproduction of polyvinyl btuyral resins exhibiting satisiactory color andodor characteristics. The invention further provides a satisiactorymethod for conducting a water suspension stabilization oi polyvinylbutyral resins to yield a product possessing substantially no odor andsatisfactory color stability characteristics. The stabilized resins ofthe present invention may be employed for all uses for which polyvinylbutyral resins are known to be useful, and are particularly well suitedfor use as ingradients in water proof coating compositions and the likewhere stable resinous materials possessing substantially no odor arerequired.

This application is a continuation-in-part of applicant's copendingapplication Serial No. 513,027, filed December 9. 1943, and nowabandoned. and entitled "Stabilization of polyvinyl acetal resins."

As many apparently widely difierent embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

I claim:

1. Process of treating a crude, water-insoluble polyvinyl butyral resinwhich comprises suspending said resin in finely divided form in apreponderantly water solution maintained at a pH of 8.0-7.5 and analkalinity of between 100 and 200, said solution containing, after saidresin is substantially neutralized, at least 0.04%, by weight or saidresin, a saturated aliphatic amine containing from 2 to 8 carbon atoms,inclusive. and having two primar amino groups.

2. Process 0! treating a crude, water-insoluble polyvinyl butyral resinwhich comprises suspending said resin in finely divided form in apreponderantly water solution maintained at a pH of 8.0-7.5, analkalinity or between 100 and 200, and

resin is substantially neutralized. at least 0.04

- by weight of said resin, of a saturated aliphatic amine containingfrom 2 to 6 carbon atoms, inclusive, and having two primary aminogroups, and further subjecting said resin to the action of said watersolution until said resin is stabilized.

4. Process of treating a crude, water-insoluble polyvinyl butyral resinwhich comprises suspending said resin in finely divided form in apreponderantly water solution maintained at a pH of 6.0-7.5 and analkalinity of between and 200, dissolving in said water solution aftersaid resin is substantially neutralized, at least 0.04%, by weight ofsaid resin, or ethylenediamine, and further subjecting said resin to theaction of said water solution until said resin is stabilized.

5. Process of treating a crude, water-insoluble polyvinyl butyral resinwhich comprises suspending said resin in finely divided form in apreponderantly water solution maintained at a pH of 6.0-7.5 and analkalinity of between 100 and 200, dissolving in said water solutionafter said resin is substantially neutralized, at least 0.04%, by weightor said resin, or diethylenetriamine, and further subjecting said resinto the action oi said water solution until said resin is stabilized.

GELU S. STAMATOFF.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,258,410 Dahle Oct. 7, 19412,282,026 Bren May 5, 1942 2,282,057 Hopkins May 5, 1942 2,332,896D'Alelio Oct. 26, 1943 OTHER REFERENCES Standard Methods for theExamination of Water and Sewage, pp. 64-66. 8th edition (1936), AmericanPublic Health Association, New York.

Certificate of Correction Patent No. 2,456A62. December 14, 1948. GELUS. STAMATOFF It is hereby certified that errors appear in the printedspecification of the above numbered patent requiring correction asfollows:

Column 1, line 10, for the word ester read esters; column 5, line 8,after -during insert the; column 6, line 18, for promphenol readbromphenol; column 7, line 16, for btuyral read butyral;

and that the said Letters Patent should be read with these correctionstherein that the same may conform to the record of the case in thePatent Ofiice.

Signed and sealed this 12th day of April, A. D. 1949.

THOMAS F. MURPHY,

Assistant Oommz'ssz'oner of Patents.

